A power supply system of the aforementioned type is known. Each switching arm of the protective device also includes a resistance connected in series to two thyristors connected head-to-tail. The resistor makes it possible to reduce the over-currents of the rotor current and limit the oscillations of the engine torque. The maximum value of this resistance is chosen to avoid the conduction of the diodes of the rotor converter during the fault.
When an over-voltage or an over-current of the power current of the engine is detected, the thyristors of the protective device are placed and kept in conduction to short-circuit the element of the electric machine and thereby protect it from the over-voltage or over-current. The thyristors of the protective device are blocked, in order to eliminate the short-circuit at the terminals of the element of the electric machine to power said element again via the power supply system.
When a thyristor is on, the blocking of the thyristor only occurs when its current cancels itself out and its polarization voltage is negative. As a result, the duration necessary to block the thyristors of the protective device is important to pick up the control of the machine more quickly, due to the significant period of time necessary to dissipate the current in the resistor.